High-speed degree-of-polarization imaging with a ferroelectric liquid-crystal modulator

Abstract

Images describing polarimetric characteristics of objects are more and more used when studying complex scenes. In some cases, only the depolarization phenomenon, mostly due to scattering, proves of interest and estimating the degree of polarization ͑DOP͒ is sufficient. For a linearly polarized beam under normal incidence, when the materials in the scene exhibit neither birefringence nor dichroism, this comes down to an intensity measurement in two crossed directions. Nevertheless, the classical optical setup, consisting mainly of a rotating polarizer used as a polarization state analyzer, gives good-quality images, but cannot provide dynamic information. In this paper, we propose to use a ferroelectric liquid-crystal modulator in an imaging polarimeter. We demonstrate the use of this modulator as a polarization state analyzer for frame rates up to about 400 Hz. Provided a fast camera is used, we show that the polarimeter allows us to surpass the classical video frame rate. We propose a setup using a rapid CCD camera ͑up to 233 Hz͒. Images in DOP are of very high quality and hold their own against images obtained with a classical polarizer. With a faster camera, we were able to obtain images at up to 400 Hz.

Optical properties of a mesogen by image analysis

“…where I 0 , I 90 , I 45 , I -45, I r and I l are, respectively, the intensities of the textures obtained from the vertical, horizontal, ±45 • , and right and left circular polarisation states [23,24]. The degree of polarisation of S-MB-nB-BC (n = 16 and 18) was calculated using Equations (2) and (3).…”

High speed partial Stokes imaging using a ferroelectric liquid crystal modulator

“…In this previous configuration, only two controls corresponding to grey levels 0 and 255 were required to drive the modulator [30]. Partial Stokes vector requires an additional control in order to get an intermediate polarization rotation, but due to the modulator nonlinear response, the corresponding grey level has been determined thanks to a full Mueller matrix characterization.…”

Customized Depolarization Spatial Patterns With Dynamic Retardance Functions

“…Partially polarized light can be expressed as a superposition of fully polarized light and unpolarized light weighted by its degree of polarization (DoP). The DoP provides very valuable additional information in the polarimetric analysis of samples [6], which is becoming especially relevant in biomedical samples where depolarization measurements can provide valuable information [7][8][9]. The term depolarization refers to the temporal and/or spatial incoherent coupling of polarized light into unpolarized light and is associated with a reduction in the DoP.…”